Scanning lidar system and method with spatial filtering for reduction of ambient light

ABSTRACT

According to one aspect, an optical transceiver includes a substrate and a laser fixed to a first surface of the substrate, the laser generating output light for transmission along a transmission axis into a region. An optical detection element is fixed to a second surface of the substrate opposite the first surface, the optical detection element receiving input light reflected from the region along a reception axis through an opening in the substrate between the first and second surfaces of the substrate, the transmission axis and the reception axis being substantially parallel.

RELATED APPLICATIONS

This application is a continuation-in-part of copending U.S. patentapplication Ser. No. 15/813,404, filed on Nov. 15, 2017, of the sameApplicant as the present application, the entire contents of which areincorporated herein by reference.

This application relies for priority on U.S. Provisional PatentApplication No. 62/623,589, filed on Jan. 30, 2018, of the sameApplicant as the present application, the entire contents of which areincorporated herein by reference.

BACKGROUND 1. Technical Field

The present disclosure is related to LiDAR detection systems and, inparticular, to a scanning LiDAR system and method with spatial filteringfor reducing ambient light.

2. Discussion of Related Art

A typical LiDAR detection system includes a source of optical radiation,for example, a laser, which emits light into a region. An opticaldetection device, which can include one or more optical detectors and/oran array of optical detectors, receives reflected light from the regionand converts the reflected light to electrical signals. A processingdevice processes the electrical signals to identify and generateinformation associated with one or more target objects in the region.This information can include, for example, bearing, range, velocity,and/or reflectivity information for each target object.

One very important application for LiDAR detection systems is inautomobiles, in which object detections can facilitate various features,such as parking assistance features, cross traffic warning features,blind spot detection features, autonomous vehicle operation, and manyother features. In automotive LiDAR detection systems, it is importantto be able to detect both bright objects at close range andlow-reflectivity objects at long range with the same systemconfiguration.

SUMMARY

According to one aspect, an optical transceiver device is provided. Theoptical transceiver device includes a substrate and a laser fixed to afirst surface of the substrate, the laser generating output light fortransmission along a transmission axis into a region. An opticaldetection element is fixed to a second surface of the substrate oppositethe first surface, the optical detection element receiving input lightreflected from the region along a reception axis through an opening inthe substrate between the first and second surfaces of the substrate,the transmission axis and the reception axis being substantiallyparallel.

In some exemplary embodiments, the transmission axis and the receptionaxis are substantially the same axis.

In some exemplary embodiments, the optical transceiver device furthercomprises a mask having at least one slit aligned with the opening ofthe substrate, such that the reflected light received by the detectionelement from the region passes through the slit. The mask can be formedat the first surface of the substrate. Alternatively, the mask can beformed at the second surface of the substrate.

In some exemplary embodiments, the optical transceiver device furthercomprises a bandpass filter, the light returning from the regionimpinging on the bandpass filter such that the light returning from theregion is filtered by the bandpass filter. The bandpass filter can havea wavelength pass band which drifts with temperature, the bandpassfilter being selected such that temperature drift of the pass band ofthe bandpass filter is determined according to temperature drift of awavelength of the output light.

In some exemplary embodiments, the optical detection element comprises asilicon photomultiplier (SiPM) detector. In other exemplary embodiments,the optical detection element comprises a multi-pixel photon counter(MPPC) detector. In some exemplary embodiments, the optical transceiverdevice further comprises a mask having at least one slit aligned withthe aperture of the substrate, such that the reflected light received bythe detector from the region passes through the slit before it reachesthe detector. The mask can be formed at the first surface of thesubstrate. Alternatively, the mask can be formed at the second surfaceof the substrate.

In some exemplary embodiments, the optical transceiver device furthercomprises a polarizing beam splitter in an optical path between thelaser and the detector, both the output light and the input light atleast partially passing through the polarizing beam splitter.

In some exemplary embodiments, the optical transceiver device furthercomprises a polarizing beam splitter in an optical path between thelaser and the detector, at least one of the output light and the inputlight at least partially passing through the polarizing beam splitter.

In some exemplary embodiments, the optical transceiver device furthercomprises a plurality of lasers fixed to a first surface of thesubstrate, the output light including a respective plurality of lightbeams generated by the plurality of lasers. In some exemplaryembodiments, the optical transceiver device further comprises a scanningdevice for scanning the plurality of light beams over the region. Thescanning device can comprise a scanning mirror. The scanning mirror canbe a micro-electromechanical system (MEMS) scanning mirror.

In some exemplary embodiments, the optical detection element comprisesan array of optical detectors. The optical detectors can comprise asilicon photomultiplier (SiPM). The optical detectors can comprise amulti-pixel photon counter (MPPC). The array of optical detectors can bea two-dimensional array.

The optical transceiver device can be part of an automotive LiDARdetection system. The LiDAR detection system can be a coaxial system.

According to another aspect, an optical transceiver devices is provided.The optical transceiver device includes a first substrate and a laserfixed to the first substrate, the laser generating output light fortransmission along a transmission axis into a region. The opticaltransceiver device also includes a second substrate and a supportstructure fixed to the first and second substrates, the supportstructure mechanically supporting the first and second substrates. Anoptical detection element is fixed to the second substrate, the opticaldetection element receiving input light reflected from the region alonga reception axis through an opening in the support structure. A maskhaving at least one slit is fixed to the support structure, the slitbeing aligned with the opening in the support structure, such that thereflected light received by the optical detection element from theregion passes through the slit before it reaches the optical detectionelement.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure is further described in the detailed descriptionwhich follows, in reference to the noted plurality of drawings by way ofnon-limiting examples of embodiments of the present disclosure, in whichlike reference numerals represent similar parts throughout the severalviews of the drawings.

FIG. 1 includes a schematic functional block diagram of a scanning LiDARsystem, according to exemplary embodiments.

FIGS. 2A and 2B include schematic functional diagrams illustratingportions of the scanning LiDAR system of FIG. 1. Specifically, FIGS. 2Aand 2B illustrate scanning of transmitted optical signals into a regionand reception of returning optical signals for a first angular directionof scanning of a scanning mirror and a second opposite angular scanningdirection the scanning mirror, respectively, according to exemplaryembodiments.

FIG. 3 includes a schematic diagram of a receive subsystem of thescanning LiDAR system of FIGS. 1, 2A and 2B, according to exemplaryembodiments.

FIG. 4 includes a schematic diagram of a mask in the receive subsystemof FIG. 3, according to exemplary embodiments.

FIG. 5 includes a schematic elevational view of a portion of a detectorarray in the receive subsystem of FIG. 3, according to exemplaryembodiments.

FIG. 6 includes a schematic functional block diagram of a scanning LiDARsystem, in which horizontal and vertical scanning are performed,according to exemplary embodiments.

FIG. 7 includes a schematic diagram of a receive subsystem of thescanning LiDAR system of FIG. 6, in which horizontal and verticalscanning are performed, according to exemplary embodiments.

FIG. 8 includes a schematic diagram illustrating the pattern of lightbeams scanned over the detector array of the receive subsystem of FIG.7, in the case in which vertical and horizontal scanning are performed,according to exemplary embodiments.

FIGS. 9A and 9B include schematic diagrams illustrating portions of ascanning LiDAR system in which a coaxial configuration is implemented,according to some exemplary embodiments.

FIGS. 10A and 10B include schematic diagrams illustrating portions ofscanning LiDAR systems in which a coaxial configuration is implemented,according to some exemplary embodiments.

FIG. 11 includes a schematic diagram illustrating any of the coaxialscanning LIDAR systems described herein, according to some exemplaryembodiments.

FIG. 12 includes a schematic diagram illustrating a portion of ascanning LiDAR system in which a coaxial configuration is implemented,according to some exemplary embodiments.

FIGS. 13A and 13B include schematic cross-sectional diagrams whichillustrate two configurations of coaxial scanning LiDAR systems, inwhich discrete lasers and discrete detectors are used, according to someexemplary embodiments.

FIG. 14A includes a schematic cross-sectional diagram which illustratesa configuration of a coaxial scanning LiDAR system, according to someexemplary embodiments.

FIG. 14B includes a schematic top view of the coaxial scanning LiDARsystem of FIG. 14A, according to some exemplary embodiments.

FIGS. 15A and 15B include schematic top views of a portion of a scanningLiDAR system, using multiplexing of lasers in a plurality of multi-laserarrays and a plurality of detectors, according to some exemplaryembodiments.

FIG. 16A includes a schematic perspective view which illustrates aconfiguration of a coaxial scanning LiDAR system 1000, according to someexemplary embodiments.

FIG. 16B includes a schematic cross-sectional view of the coaxialscanning LiDAR system of FIG. 16A, according to some exemplaryembodiments.

FIG. 16C includes a schematic top view of the coaxial scanning LiDARsystem of FIGS. 16A and 16B, according to some exemplary embodiments.

FIG. 17 includes a schematic perspective view of an automobile equippedwith one or more LiDAR systems described herein in detail, according tosome exemplary embodiments.

FIG. 18 includes a schematic top view of an automobile equipped with twoLiDAR systems as described herein in detail, according to some exemplaryembodiments.

DETAILED DESCRIPTION

The scanning LiDAR detection system described herein in detail can be ofthe type described in copending U.S. patent application Ser. No.15/410,158, filed on Jan. 19, 2017, of the same assignee as the presentapplication, the entire contents of which are incorporated herein byreference. According to the exemplary embodiments, the scanning LiDARdetection system of the present disclosure combines wide field of viewwith long detection range and high resolution. To achieve this in abiaxial system, i.e., a system in which the transmission optical axis isnot the same as the reception optical axis, various features arecombined in the system.

For example, the present system includes a high-sensitivity detectorthat can detect the relatively small number of photons reflected backfrom long range. Also, the detection device, i.e., detector array, ofthe present system is of relatively large size, thus providing anoptical aperture collecting returning light from a relatively wide fieldof view. The detection system, i.e., detector array, of the presentdisclosure has relatively high bandwidth to allow capture of arelatively short-duration light pulse. In some particular exemplaryembodiments, the waveform is a pulsed frequency-modulatedcontinuous-wave (FMCW) signal having a pulse repetition frequency (PRF)of 50-150 MHz. At 50% duty cycle, the light pulse duration can be 3.3-10ns, which is captured by the high-bandwidth detector array of thedisclosure.

Additionally, it is known that ambient light, such as sunlight, cancause shot noise in the detection system. According to the presentdisclosure, the amount of ambient light, e.g., sunlight, impinging onthe detection system is substantially reduced. Dynamic range ismaximized such that both bright objects at short distance andlow-reflectivity objects at long range can be detected with the sameconfiguration.

Thus, the scanning LiDAR system of the disclosure reduces the amount ofambient light and the signal light from objects at short distance thatcan reach the detection system by means of spatial filtering matchingthe far field laser pattern. This enables the combination of a largesensitive detector, a narrow laser beam and high signal-to-noise ratio(SNR) at long range in daytime conditions.

According to the present disclosure, a fixed or moving mask ispositioned in the focal plane of a receiver lens in the detectionsystem, i.e., LiDAR sensor. The mask includes a set of slits and isaligned with the scan pattern of the transmitter. This enables the useof avalanche photodiode detectors (APDs) in the optical detector array.In alternative embodiments, silicon photomultipliers (SiPMs), alsoreferred to as multi-pixel photon counters (MPPCs) can be used in theoptical detector array. The SiPM array is an array of light-sensitivemicrocells, each in a binary single photon counting mode. Alternatively,APDs in the array are analog components, i.e., not operated inGeiger/photon counting mode. The array provides a very high gain over alarge detector area combined with analog output and large bandwidth.

The LiDAR system of the present disclosure reduces ambient light by afactor of 5 to 500, and typically by a factor of 5 to 50. This resultsin increased SNR and increased range in daytime conditions. The systemincreases dynamic range due to focus change with respect to distance.The effective sensitivity of the APDs or SiPMs is increased, in the caseof SiPMs, due to the non-linearity of the components. According to someexemplary embodiments, with the LiDAR system of the disclosure focusedat infinity, the focal plane of the lens coincides with the slits in themask. The focus shifts as the distance to a target object changes. Atlong range, the image plane will coincide with the focal plane of thelens, where the mask is placed. At closer range, the image plane willmove away from the focal plane of the lens, i.e., further from the lens.This means that a significant amount of light will be blocked by theslit, and, therefore, the signal level at close range is substantiallyreduced, leading to increased dynamic range.

FIG. 1 includes a schematic functional block diagram of a scanning LiDARsystem 100, according to exemplary embodiments. Referring to FIG. 1,system 100 includes a digital signal processor and controller (DSPC)102, which performs all of the control and signal processing required tocarry out the LiDAR detection functionality described herein in detail.An optical source 104 operates under control of DSPC 102 via one or morecontrol signals 116 to generate the one or more optical signalstransmitted into a region 106 being analyzed. Among other functions,control signals 116 can provide the necessary control to perform waveshaping such as, in some exemplary embodiments, pulsedfrequency-modulated continuous-wave (FMCW) modulation envelope controlto produce the pulsed FMCW optical signal of some exemplary embodiments.Optical source 104 can include a single laser, or optical source 104 caninclude multiple lasers, which can be arranged in a one-dimensional ortwo-dimensional array. One or more optical signals 108 from source 104,which can be the pulsed FMCW optical signal of some exemplaryembodiments, impinge on scanning mirror 110, which can be amicroelectromechanical system (MEMS) scanning mirror. Scanning mirror110 is rotatable about an axis 114 by an actuator 112, which operatesunder control of one or more control signals 117 provided by DSPC 102 tocontrol the rotation angle of scanning mirror 110, such that the one ormore output optical signals are scanned at various angles into region106. The output optical signals pass through a lens or glass plate 122,which generates one or more collimated optical signals which are scannedacross region 106.

Returning optical signals 125 are received from region 106 at receivesubsystem 118. Receive subsystem 118 includes a lens 120 which receivesand focuses light 125 returning from region 106. According to exemplaryembodiments, mask 124 is located at the focal plane of lens 120, suchthat the returning light is focused at mask 124. Light passing throughmask 124 impinges on optical detector array 126, which, in someexemplary embodiments, can include SiPM or MPPC photomultipliers.Detector array 126 converts the received optical signals to electricalsignals, and a processor 128 generates digital signals based on theelectrical signals and transmits the digital signals 130 to DSPC 102 forprocessing to develop target object identification, tracking and/orother operations. Reports of detections to one or more user interfacesor memory or other functions can be carried out via I/O port 132.

FIGS. 2A and 2B include schematic functional diagrams illustratingportions of scanning LiDAR system 100 of FIG. 1, according to exemplaryembodiments. FIGS. 2A and 2B illustrate scanning of the transmittedoptical signals into region 106 and reception of returning opticalsignals for a first angular direction of scanning of scanning mirror 110about axis 114 and a second opposite angular scanning direction ofscanning mirror 110 about axis 114, respectively.

Referring to FIGS. 1, 2A and 2B, optical source 104 can include one ormore linear arrays of lasers disposed along parallel axes. That is, eachlinear array of lasers includes a plurality of lasers disposed along avertical axis, i.e., a y-axis. In the exemplary embodiment illustratedin FIGS. 2A and 2B, two linear arrays are disposed along parallel axesin the y-axis direction. The axes are displaced along a horizontal axis,i.e., an x-axis. Also, the two linear laser arrays are displaced also inthe vertical direction (y-axis) in order to generate different elevationangles. Alternatively, the linear laser arrays could be rotated aroundthe x-axis in order to generate different elevation angles. Thus, asillustrated in FIGS. 2A and 2B, the two parallel linear laser arrayscreate a two-dimensional array of laser outputs transmitted orthogonalto the x-y plane. In some particular exemplary embodiments, each of twolinear arrays includes 8 lasers disposed along the y-axis, for a totalof 16 lasers in the two-dimensional array. It will be understood thatany number of lasers can be used, in accordance with the presentembodiments. For example, in some particular exemplary embodiments, twolinear arrays of 11 lasers, i.e., a total of 22 lasers, are used.

Continuing to refer to FIGS. 1, 2A and 2B, in some exemplaryembodiments, the optical output signals from the laser array in source104 are focused by a lens 111 onto MEMS scanning mirror 110. The opticalsignals are reflected from scanning mirror 110 through glass plate orlens 122, which generates the substantially mutually parallel collimatedoptical output signals 123. Controlled rotation of scanning mirror 110via actuator 112 and DSPC 102 scans the collimated optical outputsignals 123 over region 106. Output signals or beams 123 constitute afan of beams 123, where each beam is collimated. In some particularexemplary embodiments, the fan angle can be 15° to 22°. In somealternative embodiments, beams 123 are substantially mutually parallel.Light 125 returning from region 106, for example, light reflected fromone or more target objects, is received at lens 120 of receive subsystem118. Lens 120 focuses the returning light 125 onto mask 124, which ispositioned in front of optical detector array 126, which, as illustratedin FIGS. 2A and 2B, can be, for example, a 32×8 array of APDs. As notedabove the detectors in detector array 126 can also be SiPMs. Thus, inthe particular illustrated exemplary embodiments, 32×8 SiPM detectorsare arranged to provide a focal plane detector. Detector array 126converts the received optical signals to electrical signals, andprocessor 128 generates digital signals based on the electrical signalsand transmits the digital signals 130 to DSPC 102 for processing todevelop target object identification, tracking and/or other operations.Reports of detections to one or more user interfaces or memory or otherfunctions can be carried out via I/O port 132.

Thus, as illustrated in FIGS. 2A and 2B, in some particular exemplaryembodiments, two arrays of 1×8 lasers are used to generate 16 individuallaser beams, each beam with a nominal divergence of <0.1°. The verticaldivergence of the group of 8 beams is nominally approximately 15°.Scanning mirror 110 is controlled to scan across a nominal range ofapproximately 60°, i.e., ±30° from its centered position. These angularlimits are illustrated in FIGS. 2A and 2B in the diagrams of the x-yplane. FIG. 2A illustrates the case in which the output optical signals123 are scanned in a first direction (to the right in FIG. 2A) viaangular rotation of scanning mirror 110 in a first angular direction,and FIG. 2B illustrates the case in which the output signals 123 arescanned in a second direction (to the right in FIG. 2B) via angularrotation of scanning mirror 110 in a second angular direction. Theresulting returning optical signals are scanned across the columns ofthe 32×8 detector array 126 illuminating pixels in the array in apredetermined order determined by the scanning of the output opticalsignals 123 into region 106, as illustrated in the schematicillustrations of pixel illumination scanning 137 and 139 in FIGS. 2A and2B, respectively. It will be understood that all of these parameters areexemplary nominal values. According to the present disclosure, anynumber of lasers can be used, having a group beam divergence of greaterthan or less than 15°, and the angular scanning limits can be greaterthan or less than ±30° from the centered position of scanning mirror110.

According to the exemplary embodiments, since detector array has 8detectors in the vertical (y) direction, only one vertical linear array,i.e., column, is turned on at a time. That is, detector array 126 isread out one column at a time, in synchronization with the laser scan.This time multiplexing provides a “rolling shutter” which limits theinfluence of environmental light, i.e., sunlight, since only one columnof detectors is receiving at a time. Additionally, mask 124, implementedin the form of a two-dimensional array of slits, is placed in front ofdetector array 126 to reduce further the amount of ambient lightreaching detector array 126.

FIG. 3 is a schematic diagram of receive subsystem 118, according toexemplary embodiments. Referring to FIG. 3, and with reference to theforegoing detailed description of FIGS. 1, 2A and 2B, light 125returning from region 106 impinges on lens 120. Mask 124 is placed atthe focal plane of lens 120, such that light 125 is focused at mask 124.Light passing through mask 124 is received at detector array 126.

FIG. 4 includes a schematic diagram of mask 124, according to someexemplary embodiments. Mask 124 includes an optically opaque portion 140and a plurality of optically transparent horizontal slits 142 a-142 p.It is noted that the use of 16 slits is consistent with the particularillustrative exemplary embodiment described herein in which light source104 includes two linear arrays of 8 lasers each. It will be understoodthat where a different laser configuration or quantity is used, mask 124would include a different number of slits 142. For example, in the casein which source 104 includes two linear arrays of 11 lasers, mask 124would include 22 slits 142.

Referring to FIG. 4, it is noted that alternating slits 142 areassociated with the same linear laser array in source 104. That is,specifically, each of alternating slits 142 a through 142 h isassociated with returning light generated by a respective one of theeight lasers in one of the vertical linear arrays of lasers in source104, and each of alternating slits 142 i through 142 p is associatedwith returning light generated by a respective one of the eight lasersin the other of the vertical linear arrays of lasers in source 104. Inaccordance with some exemplary embodiments, the linear arrays of lasersof source 104 are offset vertically with respect to each other. As aresult, the alternating groups of slits 142 a-142 h and 142 i-142 p areoffset vertically with respect to each other on mask 124, such thatreturning light associated with each laser is in alignment with itscorresponding slit.

Mask 124 can be made of one of various possible materials, such asplastic, metal, metal foil, or other material. Slits 142 can be formedin mask 124 by laser. In other embodiments, opaque portion 140 and slits142 can be formed by photolithographic processes. For example, theopaque portion 140 can be formed of an optically sensitive opaquematerial, and slits 142 can be formed by selective exposure of theoptically sensitive opaque material, e.g., through a patterned mask,followed by appropriate developing and further processing to generatethe transparent slits 142.

FIG. 5 includes a schematic elevational view of a portion of detectorarray 126, according to some exemplary embodiments. Referring to FIG. 5,eight rows of four detectors 126 a are illustrated. That is, 32 of the256 detectors 126 a in detector array 126 are illustrated for clarity ofillustration and description. As described above, according to thepresent disclosure, each of detectors 126 a can be an APD or SiPM. FIG.5 also illustrates the received pulses of light 125 returning fromregion after being focused by lens 120 and passing through slits 142 inmask 124. These received pulses appear in FIG. 5 as broken lines alongarray 126 of detectors 126 a. Specifically, broken lines 152 a through152 h illustrate pulses of returning light 125 impinging on array 126after passing through slits 142 a through 142 h, respectively, of mask140. Similarly, broken lines 152 i through 152 p illustrate pulses ofreturning light 125 impinging on array 126 after passing through slits142 i through 142 p, respectively, of mask 140. Thus, referring to FIGS.1-5, because of the vertical, y-axis offset between the linear arrays oflasers in source 104, each detector 126 a of array 126 receives andprocesses light from a plurality of lasers, e.g., two lasers asillustrated in FIG. 5, the light passing through a respective pluralityof slits 142, e.g., two slits, in mask 124.

Thus, according to the present disclosure, in some exemplaryembodiments, mask 124 having 2N horizontal slits is placed in front ofdetector array 126 of detectors 126 a, the array 126 having N detectors126 a in the vertical, i.e., y, direction. Mask 124 is aligned with thescan pattern of 2N horizontally alternately scanning laser beams.Continuing to refer to FIG. 5, in some particular exemplary embodiments,slits 142 could be as small as the diffraction limit allows, i.e., λ Xf-number ˜1 μm. In some embodiments, the width of slits 142 can be ˜0.1mm, due to alignment tolerances. With two 0.1 mm slits 142 per 1 mm²detector element 126 a, ambient light is reduced by a nominal factor of5, but a factor of ˜500 is also possible.

According to the exemplary embodiments, array 126 is an array of APDs orSiPMs, which provide certain advantages and improvements. For example,the large size and short response time of the detector elements 126 aprovide array 126 with a large detection area. This in turn enables alarge light-collecting aperture of the receiving subsystem lens. Theincreased light provides better signal-to-noise ratio (SNR) and longerrange. Also, with mask 124 in focus, but detector array 126 out offocus, local saturation of detector elements 126 a is avoided. Thisresults in increased dynamic range and further increased performance inhigh levels of ambient light.

According to the exemplary embodiments, with mask 124 in the focal planeof lens 120, all signal light passes through slits 142 in mask 124 atlong distances. Without mask 124, the optical signal intensity wouldvary inversely with the square of the distance. Therefore, at shortrange, signal intensity would be extremely high, which can cause a dropin system dynamic range. With mask 124 inserted as described herein indetail, only a small fraction of the returning light at short distancespasses through slits 142, which eliminates the reduction in dynamicrange caused by light returning from short-range target objects.

In some embodiments, in addition to horizontal scanning as describedabove in detail, scanning can also be carried out vertically. Thevertical scanning can be performed in order to increase verticalresolution. FIG. 6 includes a schematic functional block diagram of ascanning LiDAR system 100A, in which horizontal and vertical scanningare performed, according to exemplary embodiments. FIG. 7 includes aschematic diagram of receive subsystem 118A in scanning LiDAR system100A of FIG. 6, in which horizontal and vertical scanning are performed,according to exemplary embodiments. Referring to FIGS. 6 and 7, elementsthat are substantially the same as those in FIGS. 1, 2A, 2B and 3 areidentified by the same reference numerals. Referring to FIGS. 6 and 7,in this embodiment, actuator 112A, in addition to initiating andcontrolling horizontal scanning of scanning mirror 110A about verticalaxis 114, initiates and controls vertical scanning of scanning mirror110A about horizontal axis 114A. In this alternative embodiment, mask124 is also moved vertically alternately up and down in synchronizationwith the vertical scanning of scanning mirror 110A, as indicated byarrow 200 in FIG. 7. Vertical movement of mask 124 is initiated by amechanical actuation device, such as a piezoelectric actuator 202, insynchronization with scanning of scanning mirror 110A, such thatalignment of slits 142 of mask 124 with returning light 125 ismaintained. This synchronization is accomplished via interface 204 withDSPC 102.

FIG. 8 is a schematic diagram illustrating the pattern of light beamsscanned over detector array 126, in the case in which vertical andhorizontal scanning are used, according to exemplary embodiments.Referring to FIG. 8, in some embodiments, as illustrated by the scanpattern, at the end of each horizontal scan line, scanning mirror 110Ais rotated one step vertically. At the same time, mask 124 is movedvertically to ensure alignment of slits 142 in mask 124. This process ofhorizontal scan lines separated by vertical scanning increments resultsin the serpentine pattern of light beams impinging on detector array126, as illustrated in FIG. 8.

In the foregoing detailed description, scanning LiDAR systems 100, 100Aof the exemplary embodiments are shown as having biaxial configurations.That is, systems 100, 100A are illustrated and described as havingseparate output (transmission) axes and input (reception) axes. Outputsignals 123 are transmitted into region 106 along a first axis, andreturning light signals 125 are received from region 106 along a secondaxis different than the first axis. The present disclosure is alsoapplicable to coaxial system configurations in which the input andoutput axes are substantially the same.

FIGS. 9A and 9B include schematic diagrams illustrating portions of ascanning LiDAR system 200 in which a coaxial configuration isimplemented, according to some exemplary embodiments. FIG. 9Aillustrates a single coaxial configuration, and FIG. 9B illustratesmultiple coaxial configurations in parallel. Referring to FIGS. 9A and9B, a laser light source 304 integrated on or in a substrate 306generates an output beam of light. The output beam is reflected by apolarizing beam splitting cube 302 such that output signals 323 aretransmitted into region 106. Returning light signals 325 from region 106are transmitted through beam splitting cube 302, through an opening 308in substrate 306. The light may pass through an optional bandpass filter305, which further reduces the ambient light. In some exemplaryembodiments, bandpass filter 305 is characterized by a drift in itswavelength pass band which is dependent on temperature. Laser lightsource 304 can also have a temperature-dependent drift in wavelength ofits output. In some exemplary embodiments, the temperature drift oflaser light source 304 and that of bandpass filter 305 are matched, suchthat temperature effects on operation of the overall system aresubstantially reduced.

FIGS. 10A and 10B include schematic diagrams illustrating portions ofscanning LiDAR systems 300A and 300B, respectively, in which a coaxialconfiguration is implemented, according to some exemplary embodiments.The primary difference between systems 300A, 300B of FIGS. 10A and 10Bis that, in system 300A, mask 324 is under substrate 306, and, in system300B, mask 324 is at the top side of substrate 306. In both systems 300Aand 300B, incoming light from polarizing beam splitting cube 302 passesthrough slits 342 in mask 324 and impinges on APD or SiPM detector 326.In the embodiments of FIGS. 10A and 10B, lens 322 generates thesubstantially mutually parallel collimated optical output signals 323A.Controlled rotation of the scanning mirror scans the substantiallymutually parallel collimated optical output signals 323A over the regionbeing analyzed.

FIG. 11 includes a schematic diagram illustrating any of systems 200,300A, 300B, illustrating the size relationship between the opening 308or slit 342 and the pupil of the laser source 304. As in the embodimentsdescribed in detail above, in the embodiment of FIG. 11, lens 322generates the collimated optical output signals 323A. Controlledrotation of the scanning mirror scans the collimated optical outputsignals 323A over the region being analyzed. Optical output signals orbeams 323A constitute a fan of beams 323A, where each beam iscollimated. In some particular exemplary embodiments, the fan angle canbe 15° to 22°. In some alternative embodiments, beams 323A aresubstantially mutually parallel.

It should be noted that polarizing beam splitting cube 302 in theembodiments described above in detail in connection with FIGS. 9A, 9B,10A, 10B and 11 need not be a cube. In alternative embodiments,polarizing beam splitting cube 302 can be replaced with a polarizingbeam splitting plate tilted at an appropriate angle with respect to theoptical paths of the respective systems.

FIG. 12 includes a schematic diagram illustrating a portion of ascanning LiDAR system 400 in which a coaxial configuration isimplemented, according to some exemplary embodiments. System 400 differsfrom systems 200, 300A and 300B in that, in system 400, no beamsplitting cube is included. Instead, laser light source 404 providesoutput light 323 in a vertical direction into region 106 through anoptical element such as birefringent crystal 409 and lens 411. Returninglight 325 passes through lens 411 and birefringent crystal 409 such thatthe returning light is shifted to pass through apertures 408 insubstrate 406 toward the detector array. Birefringent crystal 409affects the two polarization directions of the light differently. One islaterally shifted, and the other is not shifted. Hence, birefringentcrystal 409 acts as a polarizing beam splitter. Birefringent crystal 409can be made of a material such as calcite, or other similar material.

According to exemplary embodiments, a coaxial scanning LiDAR system,such as coaxial systems 200, 300A, 300B and 400 illustrated in FIGS. 9A,9B, 10A, 10B, 11 and 12, can be implemented using a selectedconfiguration which may include one or more lasers, polarizing beamsplitters, apertures or slits, filters and detectors in combination. Forexample, configurations can vary depending on the laser and aperture oropening subassembly and/or the detector type and configuration. In someembodiments, the laser or lasers can be discrete lasers. In otherembodiments, one or more arrays of multiple lasers can be used.Similarly, in the case of detectors, one or more discrete detectors,such as APDs or SiPMs, can be used. In other embodiments, one or morearrays of detectors, such as arrays of APDs or SiPMs, can be used.

FIGS. 13A and 13B include schematic cross-sectional diagrams whichillustrate two configurations of coaxial scanning LiDAR systems 600 and700, respectively, in which discrete lasers and discrete detectors areused, according to some exemplary embodiments. Referring to FIG. 13A, alaser light source 604 is integrated on or over a substrate 606, with alayer of inert spacing material 605, made of, for example, printedcircuit board (PCB) material, epoxy, metal or similar material, mountedtherebetween. Laser light source 604 generates an output beam of light607, which impinges on a beam splitting cube 602, such that outputsignals 623 are transmitted into region 106. Returning light signalsfrom region 106 are transmitted through beam splitting cube 602, througha slit 642 in mask 624 and then through opening 608 in substrate 606. Itshould be noted that beam splitting cube 602 can be a polarizing beamsplitting cube. It should also be noted that, as with the embodimentsdescribed above, beam splitting cube 602, or polarizing beam splittingcube 602, need not be a cube. It may be a beam splitting plate orpolarizing beam splitting plate tilted at an appropriate angle withrespect to the optical path(s). Light beams 625 from slit 642 passthrough opening 608 in substrate 606 and are detected by detector 626,which is mounted to the bottom side of substrate 606. In some exemplaryembodiments, detector 626 is a surface mount device mounted to thebottom surface of substrate 606. It should be noted that, in someexemplary embodiments, laser light source 604 is one of an array oflaser light sources disposed in parallel along an axis directedsubstantially normal to the page of FIG. 13A. Similarly, polarizing ornon-polarizing beam splitting cube or plate 602 can be a single longcube or plate, or multiple cubes or plates, extending along the sameaxis normal to the page. Similarly, detector 626 can be a single longdetector or array of detectors, or multiple detectors or arrays ofdetectors, extending along the same axis normal to the page. In someexemplary embodiments, detector(s) or array(s) of detectors 626 can beSiPM or MPPC detectors.

Referring to FIG. 13B, a laser light source 704 is integrated on or overa substrate 706, with a layer of inert spacing material 705, made of,for example, printed circuit board (PCB) material, epoxy, or othersimilar material, mounted therebetween. Laser light source 704 generatesan output beam of light 707, which impinges on a beam splitting cube702, such that output signals 723 are transmitted into region 106.Returning light signals from region 106 are transmitted through beamsplitting cube 702, through a slit 742 in mask 724. It should be notedthat beam splitting cube 702 can be a polarizing beam splitting cube. Itshould also be noted that, as with the embodiments described above, beamsplitting cube 702, or polarizing beam splitting cube 702, need not be acube. It may be a beam splitting plate or polarizing beam splittingplate tilted at an appropriate angle with respect to the opticalpath(s). Light beams 725 from slit 742 are detected by detector 726,which is mounted to the top side or surface of second substrate 728.First substrate 706 and second substrate 728 are mechanically supportedand properly located with respect to each other by a mounting/spacingsupport layer 709. Mounting/spacing support layer 709 can be made of,for example, a layer of inert spacing material, made of, for example,printed circuit board (PCB) material, epoxy, metal, or other similarmaterial. The physical configuration of mounting/spacing support layer709, i.e., dimensions, location, etc., are selected to provideappropriate support and stability among components such as laser lightsource 704, beam splitting cube 702, first substrate 706, secondsubstrate 728, mask 724 and slit 742, such that the performancerequirements of system 700 are met.

It should be noted that, in some exemplary embodiments, laser lightsource 704 is one of an array of laser light sources disposed inparallel along an axis directed substantially normal to the page of FIG.13B. Similarly, polarizing or non-polarizing beam splitting cube orplate 702 can be a single long cube or plate, or multiple cubes orplates, extending along the same axis normal to the page. Similarly,detector 726 can be a single long detector or array of detectors, ormultiple detectors or arrays of detectors, extending along the same axisnormal to the page. In some exemplary embodiments, detector(s) orarray(s) of detectors 726 can be SiPM or MPPC detectors.

FIG. 14A includes a schematic cross-sectional diagram which illustratesa configuration of a coaxial scanning LiDAR system 800, according tosome exemplary embodiments. FIG. 14B includes a schematic top view ofthe coaxial scanning LiDAR system 800 of FIG. 14A, according to someexemplary embodiments. Referring to FIGS. 14A and 14B, system 800includes two laser light sources or arrays of laser light sources 804A,804B on opposite sides of a first substrate or board 806. Laser lightsources 804A-1 through 804A-11 generate output beams of light 807A,which impinge on a beam splitting cube 802, such that output signals823A are transmitted into region 106. Returning light signals fromregion 106 are transmitted through beam splitting cube 802, through aslit 842A in mask 824A. It should be noted that beam splitting cube 802can be a polarizing beam splitting cube. It should also be noted that,as with the embodiments described above, beam splitting cube 802, orpolarizing beam splitting cube 802, need not be a cube. It may be a beamsplitting plate or polarizing beam splitting plate tilted at anappropriate angle with respect to the optical path(s). Light beams 825Afrom slit 842A are detected by detectors 826A-1 through 826A-11, whichare mounted to the top side or surface of second substrate 828. In someexemplary embodiments, detector(s) or array(s) of detectors 826A and826B can be SiPM or MPPC detectors.

Similarly, laser light sources 804B-1 through 804B-10 (not seen on backsurface of first substrate 806) generate output beams of light 807B,which impinge on a beam splitting cube or plate 802, such that outputsignals 823B are transmitted into region 106. Returning light signalsfrom region 106 are transmitted through beam splitting cube 802, througha slit 842BA in mask 824B. Light beams 825B from slit 842B are detectedby detectors 826B-1 through 826B-10, which are mounted to the top sideor surface of second substrate 828.

First substrate 806 and second substrate 828 are mechanically supportedand properly located with respect to each other by a mounting/spacingsupport layer 809. Mounting/spacing support layer 809 can be made of,for example, a layer of inert spacing material, made of, for example,printed circuit board (PCB) material, epoxy, metal, or other similarmaterial. The physical configuration of mounting/spacing support layer809, i.e., dimensions, location, etc., are selected to provideappropriate support and stability among components such as laser lightsources 804A and 804B, beam splitting cube or plate 802, first substrate806, second substrate 828, masks 824A and 824B, slits 842A and 842B,such that the performance requirements of system 800 are met.

Is should be noted that the exemplary embodiment of FIGS. 14A and 14Bincludes eleven (11) detectors on the top side of substrate 806 and ten(10) detectors on the bottom side of substrate 806. It will beunderstood that these quantities are selected as exemplary illustrationsonly. Other quantities of detectors can be used.

FIGS. 15A and 15B include schematic top views of a portion of a scanningLiDAR system, using multiplexing of lasers in a plurality of multi-laserarray devices 901A, 901B, 901C, 901D and a respective plurality ofdetector arrays 926A, 926B, 926C, 926D, under a respective plurality ofbeam splitting cubes or plates 902A, 902B, 902C, 902D. In some exemplaryembodiments, detector(s) or array(s) of detectors 926A, 926B, 926C, 926Dcan be SiPM or MPPC detectors. It is noted that, in the exemplaryembodiments, all of multi-laser array devices 901A, 901B, 901C, 901D arethe same. Accordingly, for ease and clarity of description and foravoidance of unnecessary redundancy, only one of the devices will bedescribed. Multi-laser array device 901A includes multiple, e.g., four(4), laser light sources 904A, 904B, 904C, 904D. The activation of eachlaser light source 904A, 904B, 904C, 904D is controlled by a respectiveactivation power and timing/control circuit 905A, 905B, 905C, 905D. Insome exemplary embodiments, activation of laser light sources 904 iscontrolled in a time-multiplexed fashion such that only a single laserlight source 904 in each multi-laser array device 901 is active at atime. As a result, only a single corresponding detector 926 is activelyreceiving signal at a time. At the instant illustrated in FIG. 15A, eachfirst laser light source 904A is active, as indicated by the laser lightbeam output from all four laser light sources 904A. At some instantlater in time, as illustrated in FIG. 15B, each fourth laser lightsource 904D is active, as indicated by the laser light beam output fromall four laser light sources 904D. This laser multiplexing approach toactivation of the laser light sources is applicable to any of theembodiments described herein.

FIG. 16A includes a schematic perspective view which illustrates aconfiguration of a coaxial scanning LiDAR system 1000, according to someexemplary embodiments. FIG. 16B includes a schematic cross-sectionalview of the coaxial scanning LiDAR system 1000 of FIG. 16A, according tosome exemplary embodiments. FIG. 16C includes a schematic top view ofthe coaxial scanning LiDAR system 1000 of FIGS. 16A and 16B, accordingto some exemplary embodiments. Referring to FIGS. 16A-16C, system 1000includes laser light sources or arrays of laser light sources 1000 on afirst substrate or board 1006. Laser light sources 1004 generate outputbeams of light which impinge on a beam splitting plate 1002, such thatoutput signals are transmitted into region 106. Returning light signalsfrom region 106 are transmitted through beam splitting cube 1002,through opening 1003 in mechanical support structure 1009, and through aslit 1042 in mask 1024 attached to a surface of mechanical supportstructure 1009. It should be noted that beam splitting plate 1002 can bea polarizing beam splitting plate. Light beams are detected by detectors1026, which are mounted to the top side or surface of second substrate1028. In some exemplary embodiments, detector(s) or array(s) ofdetectors 1026 can be SiPM or MPPC detectors.

First substrate 1006 and second substrate 1028 are mechanicallysupported and properly located with respect to each other by amechanical support structure 1009. Mechanical support structure 1009 canbe made of, for example, a layer of inert spacing material, made of, forexample, printed circuit board (PCB) material, epoxy, metal, or othersimilar material. The physical configuration of mechanical supportstructure 1009, i.e., dimensions, location, etc., are selected toprovide appropriate support and stability among components such as laserlight sources 1004, beam splitting plate 1002, first substrate 1006,second substrate 1028, mask(s) 1024, slits 1042, such that theperformance requirements of system 1000 are met.

FIG. 17 includes a schematic perspective view of an automobile 500,equipped with one or more scanning LiDAR systems 100, 100A, describedherein in detail, according to exemplary embodiments. Referring to FIG.17, it should be noted that, although only a single scanning LiDARsystem 100, 100A is illustrated, it will be understood that multipleLiDAR systems 100, 100A according to the exemplary embodiments can beused in automobile 500. Also, for simplicity of illustration, scanningLiDAR system 100, 100A is illustrated as being mounted on or in thefront section of automobile 500. It will also be understood that one ormore scanning LiDAR systems 100, 100A can be mounted at variouslocations on automobile 500. Also, it will be understood that LiDARsystem 100, 100A can be replaced with any of the LiDAR systems describedherein. That is, the description of FIG. 17 is applicable to anautomobile equipped with any of the embodiments described herein.

FIG. 18 includes a schematic top view of automobile 500 equipped withtwo scanning LiDAR systems 100, 100A, as described above in detail,according to exemplary embodiments. In the particular embodimentsillustrated in FIG. 18, a first LiDAR system 100, 100A is connected viaa bus 560, which in some embodiments can be a standard automotivecontroller area network (CAN) bus, to a first CAN bus electronic controlunit (ECU) 558A. Detections generated by the LiDAR processing describedherein in detail in LiDAR system 100, 100A can be reported to ECU 558A,which processes the detections and can provide detection alerts via CANbus 560. Similarly, in some exemplary embodiments, a second LiDARscanning system 100, 100A is connected via CAN bus 560 to a second CANbus electronic control unit (ECU) 558B. Detections generated by theLiDAR processing described herein in detail in LiDAR system 100, 100Acan be reported to ECU 558B, which processes the detections and canprovide detection alerts via CAN bus 560. It should be noted that thisconfiguration is exemplary only, and that many other automobile LiDARconfigurations within automobile 500 can be implemented. For example, asingle ECU can be used instead of multiple ECUs. Also, the separate ECUscan be omitted altogether. Also, it will be understood that LiDAR system100, 100A can be replaced with any of the LiDAR systems describedherein. That is, the description of FIG. 17 is applicable to anautomobile equipped with any of the embodiments described herein.

It is noted that the present disclosure describes one or more scanningLiDAR systems installed in an automobile. It will be understood that theembodiments of scanning LiDAR systems of the disclosure are applicableto any kind of vehicle, e.g., bus, train, etc. Also, the scanning LiDARsystems of the present disclosure need not be associated with any kindof vehicle.

Direct detection LiDAR systems are characterized by construction andfunctional simplicity and, unlike the more complex homodyne orheterodyne LiDAR systems, do not utilize frequency translation or downconversion stages, which facilitate signal detection and processing gainadvantages. The signal detection and processing gain advantages ofhomodyne/heterodyne LiDAR systems are enabled by advanced modulation andcoding of the transmitted signal combined with sophisticated correlationprocessing techniques within the LiDAR receiver. Transmit signalmodulation and coding, in conjunction with advanced correlationprocessing techniques, have been utilized within radar systems, fromcomplex military object imaging systems to commercial automotiveautonomous cruise control applications. LiDAR systems, with theexception of very advanced measurement requirements, e.g. NASAmeasurements of CO₂ emissions, have not utilized these techniques.However, according to the present disclosure, development of lasertransmit signal envelope modulation and quadrature demodulation of therecovered envelope modulation signal has exhibited similar advantages tothose associated and achieved via the radar science. Laser transmitterenvelope modulation and quadrature demodulation represent a modestincrease in complexity of direct detection LiDAR systems withsignificant benefits in measurement capability and lower operationalpower by enabling signal processing gain to direct detection LiDAR.

Whereas many alterations and modifications of the disclosure will becomeapparent to a person of ordinary skill in the art after having read theforegoing description, it is to be understood that the particularembodiments shown and described by way of illustration are in no wayintended to be considered limiting. Further, the subject matter has beendescribed with reference to particular embodiments, but variationswithin the spirit and scope of the disclosure will occur to thoseskilled in the art. It is noted that the foregoing examples have beenprovided merely for the purpose of explanation and are in no way to beconstrued as limiting of the present disclosure.

While the present inventive concept has been particularly shown anddescribed with reference to exemplary embodiments thereof, it will beunderstood by those of ordinary skill in the art that various changes inform and details may be made therein without departing from the spiritand scope of the present inventive concept as defined by the followingclaims.

1. An optical transceiver device, comprising: a substrate; a laser fixedto a first surface of the substrate, the laser generating output lightfor transmission along a transmission axis into a region; and an opticaldetection element fixed to a second surface of the substrate oppositethe first surface, the optical detection element receiving input lightreflected from the region along a reception axis through an opening inthe substrate between the first and second surfaces of the substrate,the transmission axis and the reception axis being substantiallyparallel.
 2. The optical transceiver device of claim 1, wherein thetransmission axis and the reception axis are substantially the sameaxis.
 3. The optical transceiver device of claim 1, further comprising amask having at least one slit aligned with the opening of the substrate,such that the reflected light received by the detection element from theregion passes through the slit.
 4. The optical transceiver device ofclaim 3, wherein the mask is formed at the first surface of thesubstrate.
 5. The optical transceiver device of claim 3, wherein themask is formed at the second surface of the substrate.
 6. The opticaltransceiver device of claim 1, further comprising a bandpass filter, thelight returning from the region impinging on the bandpass filter suchthat the light returning from the region is filtered by the bandpassfilter.
 7. The optical transceiver device of claim 6, wherein thebandpass filter has a wavelength pass band which drifts withtemperature, the bandpass filter being selected such that temperaturedrift of the pass band of the bandpass filter is determined according totemperature drift of a wavelength of the output light.
 8. The opticaltransceiver device of claim 1, wherein the optical detection elementcomprises a silicon photomultiplier (SiPM) detector.
 9. The opticaltransceiver device of claim 1, wherein the optical detection elementcomprises a multi-pixel photon counter (MPPC) detector.
 10. The opticaltransceiver device of claim 9, further comprising a mask having at leastone slit aligned with the aperture of the substrate, such that thereflected light received by the detector from the region passes throughthe slit before it reaches the detector.
 11. The optical transceiverdevice of claim 10, wherein the mask is formed at the first surface ofthe substrate.
 12. The optical transceiver device of claim 10, whereinthe mask is formed at the second surface of the substrate.
 13. Theoptical transceiver device of claim 1, further comprising a polarizingbeam splitter in an optical path between the laser and the detector,both the output light and the input light at least partially passingthrough the polarizing beam splitter.
 14. The optical transceiver deviceof claim 1, further comprising a polarizing beam splitter in an opticalpath between the laser and the detector, at least one of the outputlight and the input light at least partially passing through thepolarizing beam splitter.
 15. The optical transceiver device of claim 1,further comprising a plurality of lasers fixed to a first surface of thesubstrate, the output light including a respective plurality of lightbeams generated by the plurality of lasers.
 16. The optical transceiverdevice of claim 15, further comprising a scanning device for scanningthe plurality of light beams over the region.
 17. The opticaltransceiver device of claim 16, wherein the scanning device comprises ascanning mirror.
 18. The optical transceiver device of claim 17, whereinthe scanning mirror is a micro-electromechanical system (MEMS) scanningmirror.
 19. The optical transceiver device of claim 1, wherein theoptical detection element comprises an array of optical detectors. 20.The optical transceiver device of claim 19, wherein the opticaldetectors comprise a silicon photomultiplier (SiPM).
 21. The opticaltransceiver device of claim 19, wherein the optical detectors comprise amulti-pixel photon counter (MPPC).
 22. The optical transceiver device ofclaim 19, wherein the array of optical detectors is a two-dimensionalarray.
 23. The optical transceiver device of claim 1, wherein theoptical transceiver device is part of an automotive LiDAR detectionsystem.
 24. The optical transceiver device of claim 23, wherein theLiDAR detection system is a coaxial system.
 25. An optical transceiverdevice, comprising: a first substrate; a laser fixed to the firstsubstrate, the laser generating output light for transmission along atransmission axis into a region; a second substrate; a support structurefixed to the first and second substrates, the support structuremechanically supporting the first and second substrates; an opticaldetection element fixed to the second substrate, the optical detectionelement receiving input light reflected from the region along areception axis through an opening in the support structure; and a maskhaving at least one slit fixed to the support structure, the slit beingaligned with the opening in the support structure, such that thereflected light received by the optical detection element from theregion passes through the slit before it reaches the optical detectionelement.